Backplate and a method of making a backplate

ABSTRACT

A backplate supports friction material of a disc brake pad. The backplate includes a substantially planar portion of sheet metal and a stiffening flange extending around at least a portion of the periphery of the planar portion.

The present invention relates to a backplate and a method of making abackplate. More particularly, the present invention relates to abackplate and a method of making a backplate for supporting frictionmaterial of a disc brake pad, in particular, but not exclusively, foruse on heavy vehicles such as trucks.

Backplates of vehicle disc brake pads essentially perform two functions:they provide a solid support for slidably mounting the friction materialwithin the brake carrier in such a way to transmit shear loads inducedon the friction material during braking to the carrier, and theytransmit and distribute the pressure applied by brake tappets duringbraking evenly to the surface of the friction material to ensure evenwear of the friction material over its service life.

In order to perform the former of these two functions it is common forresilient means such as a leaf-type spring to hold the pad radially inthe carrier whilst permitting movement towards and away from anassociated brake disc thereby prevent rattling of the pad in use. Toensure that the friction material is securely attached to the backplate,some form of positive location is usually provided on the backplate,such as holes or recesses into which the material can extend or steelmesh welded on to the backplate around which the friction material maybe formed.

Each brake is generally provided with one or more tappets that apply thebraking force over a small area relative to the total area of thebackplate. In order to perform the function of distributing the pressurefrom the brake tappet(s) it has hitherto been necessary to provide arelatively thick solid steel backplate that is punched or otherwise cutfrom steel sheet and is resistant to bending, or alternatively toprovide an intermediate spreader plate in order to distribute the loadover a thinner, although still substantial backplate. If a thickbackplate is used, this constitutes a substantial proportion of theoverall mass of the pad when unworn (e.g. approximately 30%). Once thefriction material has been worn away in use, the backplate is usuallythrown away.

This means that any reduction in the mass of the backplate that can beachieved will result in environmental benefits and a reduction in thecost of materials. A lower backplate mass additionally means that alower strength, and therefore lower mass (and a potentially lower cost)pad spring may be sufficient to hold the backplate in place.

A further disadvantage of prior art backplates for heavy vehicles isthat high capacity stamping machines are required in their manufacture,with a consequential high capital investment being required to set up amanufacturing plant.

The present invention seeks to overcome, or at least mitigate, theproblems of the prior art.

One aspect of the present invention provides a backplate for supportingfriction material of a disc brake pad, the backplate comprising asubstantially planar portion of sheet metal and a stiffening flangeextending around at least a portion of the periphery of the planarportion.

A second aspect of the present invention provides a backplate forsupporting friction material of a disc brake pad, the backplate beingprovided with an integral spring arranged so as to resiliently resistmovement in a direction in a plane as defined by the backplate, in use.

A third aspect of the present invention provides a backplate forsupporting friction material of a brake pad for use in a heavy vehicledisc brake, the backplate comprising sheet metal, having a thickness inthe range of 1 mm to 3 mm and wherein a stiffening feature is providedin the backplate to impart sufficient strength thereto.

A further aspect of the present invention provides a method of making abackplate for supporting friction material of a disc brake padcomprising the steps of:

-   -   i) cutting a blank from a metal sheet;    -   ii) drawing the blank in a press so as to form a backplate        having a substantially planar portion and a stiffening flange        extending around at least a portion of the periphery of the        planar portion.

Embodiments of the present invention will be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of the rear face of a disc brake padincorporating a backplate according to one embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of line X-X of FIG. 1; and

FIG. 3 is a perspective view of the front of a disc brake pad accordingto second embodiment of the present invention.

Referring to FIGS. 1 and 2, a disc brake pad 10 comprises a steelbackplate 12 and sacrificial friction material 14. The friction materialmay be of any suitable known type, and does not form part of theinvention. The backplate 12 is formed of relatively thin sheet metalmaterial, typically sheet steel. Backplates according to the presentinvention for use with heavy vehicles are formed from sheet steel havinga thickness of between approximately 1 mm and 3 mm, preferablyapproximately 2 mm. This contrasts with prior art backplates, whichgenerally have a thickness of 8 mm to 9 mm.

It can be seen that the backplate comprises a substantially planar bodyportion 18 and a peripheral flange portion 16 arranged at substantially90° to the body and extending away from the friction material 14.

In this embodiment, the backplate 12 is further provided with a pair ofraised bosses 20 and 22 positioned so as to be contacted by tappets (notshown) of an actuating portion of the disc brake and thereby urge thefriction material 14 into contact with a brake disc (not shown) toeffect braking. The bosses are substantially circular in shape andcomprise two raised tappet contacting faces 30 that are substantiallyparallel to the plane of the body portion 18 and are interconnectedtherewith by skirt portions 32. In this embodiment, the skirt portions32 are substantially perpendicular to the planes of body portion 18 andfaces 30. In another embodiment, the skirt portions may be angledrelative thereto, however.

In other classes of embodiment, the number of projections 20 and 22 maybe adjusted according to the number of tappets provided on the brakeactuating portion, or a single projection may be provided for two ormore tappets. The shape and depth of the bosses may be adjusted asrequired. It may appreciated by those skilled in the art that the bosses20 and 22 serve to stiffen the backplate and distribute the load appliedby the brake tappet(s) more evenly over the friction material 14,thereby reducing the tendency of the backplate 12 and friction materialto bend. The bosses 20 and 22 advantageously assist in the positivelocation of the friction material 14 to the backplate 12, thus reducingthe risk of the friction material detaching under sheaf loads.

In a preferred embodiment of the invention, radially outwardly extendingribs 24 may be formed around the base circumference of the bosses 20 and22 that serve to further enhance the load spreading characteristicsthereof. It can be seen that in FIG. 1, four ribs 24 are provided foreach boss, but this may be adjusted according to the particularrequirements and characteristics of a backplate.

It can be further seen from FIG. 1 that the upper portion of flange 16is provided with a pair of recesses 26 and 28 that are shaped so as tolocate an appropriately dimensioned pad spring (not shown). The shape ofrecesses 26 and 28 may be altered so as to accommodate various shapes ofpad spring.

The backplate 12 is preferably manufactured from a blank of relativelythin sheet steel that is formed between appropriately contoured dies ina press so as to form the peripheral flange 16 and/or bosses 20 and 22.The backplate is preferably cold formed although hot forming is alsoenvisaged. Some localised thinning of the material may occur duringpressing but this is largely restricted to the corners where flangesformed on the radial edges and circumferential edges intersect, and tothe boss areas.

Turning now to FIG. 3, in which an alternative embodiment of backplateis shown and is which like numerals have, where possible been used todesignate like parts, with the addition of the prefix “1”. It can beseen that in this embodiment, a pad spring 134 is formed integrally withthe backplate again preferably using the press forming process describedabove. One advantage of providing an integral pad spring 134 is that theneed for a separate spring component to be manufactured is negated. Thismay provide additional cost and weight savings.

It should be understood that numerous changes may be made within thescope of the present invention. For example, the backplate may bemanufactured from materials other than steel, such as aluminium,provided the materials have appropriate strength and drawingcharacteristics. Alternative manufacturing methods may be employed suchas drop forging, fabrication, or die casting. Stiffening features otherthan a flange may be provided in the backplate and the flange may notnecessarily extend around the entire periphery of the backplate. Forexample, a flange may be provided on one or more of the radial orcircumferential edges of the backplate only. The backplate may be usedin relation to pads intended for fitment to other vehicles such as carsand the like.

An integral pad spring may be provided in backplates manufactured usingalternative methods to the drawing methods described above. The volumedefined by the peripheral flange may be at least partially filled withinsulating material so as to inhibit the transfer of friction inducedheat to the brake tappet(s), whose seals may otherwise be damaged bysuch high temperatures.

1. A backplate for supporting friction material of a disc brake pad, thebackplate comprising: a substantially planar portion of sheet metalincluding a first face that receives the friction material and a secondface: and a stiffening flange extending around an entire periphery ofthe substantially planar portion of sheet metal, wherein the stiffeningflange extends from the second face and away from the first face.
 2. Thebackplate according to claim 1 wherein the stiffening flange is disposedsubstantially perpendicular to the substantially planar portion of sheetmetal.
 3. The backplate according to claim 1 further including an innercircumferential edge and an outer circumferential edge, wherein thestiffening flange is provided on at least one of the innercircumferential edge and the outer circumferential edge of thebackplate.
 4. The backplate according to claim 1 wherein the stiffeningflange is provided on a radial edge of the backplate.
 5. (CANCELLED) 6.The backplate according to claim 1 wherein the stiffening flange ispress formed.
 7. The backplate according to any of claim 4 wherein thestiffening flange is provided with recess that receives a pad spring. 8.The backplate according to claim 1 wherein the backplate includes anintegral pad spring.
 9. A backplate for supporting friction material ofa disc brake pad, the backplate comprising: a substantially planarportion of sheet metal; a stiffening flange extending around at least aportion of a periphery of the substantially planar portion of sheetmetal; and a boss arranged to transmit a load induced by a brakeactuator to the friction material.
 10. The backplate according to claim9 wherein the boss is press formed.
 11. The backplate according to claim9 wherein the boss includes a face and a stiffening rib extending fromthe face.
 12. The backplate according to claim 11 wherein the stiffeningrib extends radially from the face.
 13. The backplate according to claim1 wherein the substantially planar portion of sheet metal has athickness between 1 and 3 mm.
 14. A backplate for supporting frictionmaterial of a disc brake pad, the backplate comprising: a flangeextending around at least a portion of a periphery of the backplate; andan integral spring arranged to resiliently resist movement in adirection substantially in a plane defined by the backplate.
 15. Thebackplate according to claim 14 wherein the integral spring is pressformed.
 16. (CANCELLED)
 17. The backplate according to claim 14 furthercomprising a press formed boss arranged to transmit a load induced by abrake actuator to the friction material.
 18. (CANCELLED)
 19. A discbrake pad comprising: friction material; and a backplate for supportingthe friction material, the backplate comprising: a substantially planarportion of sheet metal including a first face that receives the frictionmaterial and a second face; and a stiffening flange extending around anentire periphery of the substantially planar portion of sheet metal,wherein the stiffening flange extends from the second face and away fromthe first face. 20-21. (CANCELLED)
 22. A method of making a backplatefor supporting friction material of a disc brake pad comprising thesteps of: cutting a blank from a metal sheet; drawing the blank in apress to form a backplate having a substantially planar portion with afirst face that receives the friction material, a second face and astiffening flange extending around at least a portion of a periphery ofthe substantially planar portion, and the stiffening flange extends fromthe second face and away from the first face; and securing the frictionmaterial to the first face of the substantially planar portion.